The present invention relates generally to a sensor for measuring displacement, and more particularly to an optical fiber strain sensor.
It is often desirable to monitor strain in a structure, such as a bridge or highway overpass, a building, or a component in a vehicle, in order to get advance warning of fracture or other failure of the structure. However, it is not always convenient (or even necessary) to monitor the strain as it is occurring, and it is sufficient to know merely the maximum strain the structure has experienced in a given timeframe. For example, for vehicles such as aircraft, weight, space and other limitations would preclude monitoring strain of components therein in real time, but for purposes of evaluating the likelihood of future failure, it would be sufficient to know the maximum strain the component in the vehicle experienced during a particular trip. Therefore, it would be convenient to have a means of sensing and maintaining for later measurement the maximum strain the component experienced.
Optical fiber sensors for measuring strain are known in the art, and have many advantages over other types of sensors. They are economical, durable, light-weight, and can be used in electromagnetically noisy environments, and are therefore ideal for use in aircraft. Currently-used optical fiber sensors either require active and continuous recording of the strain in real time or are of the on-off type wherein the optical fiber fails at a predetermined strain level. None of them provides a maximum strain measurement without continuous monitoring.